The present invention is directed to thermoplastic mixtures of 1) polyurethanes and 2)o,o,o',o'-tetramethylbisphenol-polycarbonate and/or polycaprolactone and to the use thereof as adhesives. The mixtures may be used either as hot melt adhesives or as cold setting adhesives, depending on their composition.
The boding of shoe soles based on SBS block polymer compounds by means of polyurethane (PU) adhesives in many cases does not provide the necessary bond strength unless the soles have been given a special preliminary treatment. There have therefore been many attempts in the past to find ways to improve the bond strength.
In British patent 1,293,842, it was proposed to carry out a preliminary treatment with N-halogen compounds (such as isocyanuric chloride, 1,3-dichloro-5,5-dimethylhydantoin, N-chlorosuccinimide, or the like) on parts which are to be bonded or to add these N-halogen compounds to the adhesives. When used for the pretreatment of the parts to be bonded, these compounds are applied as primers and therefore constitute an additional working step, which is undesirable. When the N-halogen compounds are used as an additive to the adhesives, the adhesives must then be stored in the form of solutions (which is also undesirable). When such solutions are insufficiently stable, the N-halogen compounds must be added to the adhesives shortly before use (which is generally undesirable because of the halogen released by the N-halogen compounds).
According to British patent 1,500,296, mixtures of isocyanuric chloride and a sulphonamide such as, for example, p-toluene sulphonamide, can be used as primer. According to British patent 2,048,897, the reaction product of a styrene/butadiene/styrene (SBS) block polymer and N-halogen compound can be used as primer. It is known from German Offenlegungsschrift 2,454,553 to use solutions of hydroxy chlorinated SBS block polymers as primers or as mixtures with PU adhesives for bonding rubber soles. If these compounds are to be used as primers, it would be desirable to avoid the additional working step involved. The hydroxy chlorinated SBS block polymers described in the '553 reference have proved to be insoluble after their separation from organic solution and can then no longer be readily dissolved in solvents.
Thus, there has existed a demand for an adhesive which could be used for bonding shoe soles without the use of a primer, and in particular, for use in bonding soles of thermoplastic rubber based on SBS block polymer compounds. It has surprisingly been found that new mixtures described herein solve this problem.